Electrical switch



May 3, 1938. s. RUBEN ELECTRICAL SWITCH Filed July 23, 19371745251155511 1.5555519941 vidi?? l l N V E N TO R Jamue/ lue// BY lATTO R N EY Patented May 3,4v 1938 UNITED STATES PATENT GFFICEELECTRICAL SWITCH Samuel Ruben, New Rochelle, N. Y.

Application July 23, 1937, Serial No. 155,324

11 Claims.

This invention relates to electrical switches and circuit opening andclosing contact devices.

The general object of the invention is the provision of devices of thischaracter of novel operation and design, which are capable of breakingcurrents of large magnitude with negligible deterioration of theelectrical contacts, which provide the advantages of mercury contactingdevices without the disadvantages heretofore encountered in the use ofsuch devices, which insure safe and dependable operation over longperiods of time and which may be easily and economically manufactured.

A specific object of the invention is the pro- 16 vision of a time delayrelay suitable for operation in a thermal circuit breaker.

Another object is the provision of a thermostatically operated switch.

A further object is the provision of a gravity operated switch.

Still another object is the provision of an electro-magneticallyoperated switch.

Other objects will be apparent from the disclosure and from the drawingin which Fig. 1 illustrates a device of the invention in which themovable contact is operated by gravity:

l Fig. 2 shows a device in which the movable contact is mounted onathermostatic member;

Fig. 3 shows a time delay relay or circuit breaker, the movable contactbeing mounted on a thermostat adapted to move away from the xed contactand open the circuit when excess current is developed;

Fig. 4 illustrates a magnetically operated circuit breaker, the movablecontact being adapted to open or close the circuit under magneticiniiuence;

Figs. 5 and 6 are views of another form of time delay switch in whichthe current circulating through the thermostat metal causes movementthereof to open or close the circuit;

Fig. 7 shows an embodiment of the invention in a metal tube housing.

The present invention comprises an electrical circuit opening andclosing device housed in a sealed chamber, which has been highlyevacuated and which contains a mercury vapor atvmospherel At least oneof the circuit closing 50 contacts is formed of a metal whichamalgamates with mercury, so that due to the presence of the mercuryvapor, and the exclusion of air and gases from the evacuated chamber,the contact has at t all times a protecting lm of mercury on itssurface. Preferably, one or both of the contacts has an intimatelyjoined backing of a. relatively large mass of high heat conductingmetal, having a heat capacity adequate to maintain the contacttemperature below the point where complete volatilization of the mercurymight take place and capable of absorbing and dissipating the energylosses in operation.

The advantages of employing mercury as an electrode in the breaking of acontact or in opening an electrical circuit have long been known, andthe use of liquid mercury (in 'a gaseous atmosphere to preventmaintenance of an arc) to effect such breaking, has always beenconsidered necessary. In prior devices, employing a mercury contact in asealed or housed chamber, the current has been discharged through adenite path length of liquid mercury. Such prior devices have employed acooperating contact of a metal not readily amalgamable with mercury,usually iron or nickel, and in order to avoid the production of amercury arc, have usually employed an atmosphere of hydrogen. The deviceof this invention does not employ liquid mercury as a contact elementand the internal resistance drop characteristic of devices where thecurrent 25 path is through a column of liquid mercury is eliminated.Both contacts of my present device are formed of solid metal, at leastone is movable and the mercury is actively present only as a iilm whichamalgamates with and is absorbed 30 on to the surface of one or both ofthe contacts, thereby vproviding negligible contact resistance.

The rapid current-breaking operation of mercury type switches is alsoobservable in the switch of this invention, but clue to the lowelectrical resistance at the contact surfaces and the high heat capacityof the contacts, less mercury vapor is observable The snap switchaction, characteristic of the present device, even with an extremely lowspeed of contact movement, is apparently due to the presence of asurface mercury iilm on the contact; due to the low ionization potentialof mercury, any sparking at the time the circuit is opened, will tend totake place through the mercury vapor rather than through the contactmetal vapor; due to the high heat conductivity and capacity of thecontacts, an immediate condensation and de-ionization of the mercuryvapor obtains. Ordinarily, in liquid mercury switches, a high pressureinert atmosphere is necessary in order to prevent the mercury frommaintaining an arc.

The use of a relatively large mass of metal for one or both of thecontacts is highly desirable where high power is to be controlled. Thehigh heat capacity provided by the metal is necessary to avoid rise intemperature of the contacts to a point where an excessive amount ofmercury is volatilized from the contact surface. This metal membershould also preferably have the maximum radiating area so as to .be ableto rapidly dissipate the energy lost in making and breaking contact.

While in most cases it will be desirable to form the contacting surfacesof both contacts from metals of the rst periodic group which readilyamalgamate with mercury such as copper, gold, silver or alloys thereof,only one of the contacts may 'be formed from such metal and thecooperating contact may be formed from a refractory metal such astungsten or molybdenum. One forrn of contact which tenaciously holds afilm of mercury is a large copper element having a gold plated workingface. During the evacuation of the device, the contacts as well as othermetal parts are heated to as high a temperature as possible in order todrive out any cccluded gases, and this heating tends to make the platingmore adherent.` The plating may be electrodeposited or rolled on, inaccordance with well known practice.

In order to describe various embodiments of the invention, reference ismade to the drawing, in which, unless otherwise indicated, similarnumerals indicate similar parts.

In Fig. l, the highly evacuated sealed glass bulb I, housing stationarycopper contact 2, mounted on heavy heat dissipating support member 3, isconnected to terminal 4. 'I'he movable copper contact 5, having a largeflanged heat dissipating mass 6, is supported on molybdenum spring 1,which is in turn suspended from and connected to terminal 8. Mercury isheld in glass and nickel cylinder 9. In the manufacture of the device,the mercury remains in the cylinder until after the tube has beenevacuated, after which time the cylinder is inductively heated by meansof high frequency, causing the glass to soften and the pressure of themercury vapor forcing the cylinder open so that the mercury is condensedon the walls of the tube. The evacuation is preferably of a high orderin order to free the tube of gases which might cause premature sparkingor maintenance of an arc. After the tube has been sealed off, themercury will commence to form an amalgam with the copper contacts, theamalgamation taking place for a considerable depth. The heavy weight 6,provides gravity operation and contact is made or broken by merelyturning the bulb to the desired position,

In Fig. 2, movable'silver faced contact I5, is mounted on thermostaticmetal support I1, welded to terminal I8, and under the influence of heatwill move over to make contact with silver molybdenum contact member I2,mounted on support I3, welded to support I4.

In Fig. 3, gold plated copper contact 25, is mounted on bent bimetallicthermostatic element 21, and is normally positioned to maintain a closedcircuit in juxtaposition with stationary tungsten contact 22. Whenexcess current is developed so that the temperature f thermostaticelement 21, is suiiiciently raised, the switch will operate as a thermalcircuit breaker, contact 25 moving away from contact 22 and opening thecircuit.

Fig. 4 shows a circuit breaker operated externally by means of anelectromagnet. Movable tungsten silver contact 35, brazed to iron weight30, is normally in juxtaposition with heavy heatradiating silver contact32. When excess current flows through electromagnet E, the iron weight30, carrying contact 35, is attracted away from stationary contact 32,thus breaking the circuit.

Figs. and 6 are side and front views respectively, of another form ofthermostatically operated switch in which the cross section of thethermostatic metal loop member 41, is such as to give rapid heating whencurrent is discharged through each leg of the loop. Prong 44, is theterminal for stationary contact I2, and prongs 43 and 49 are terminalsfor supplying current to thermostatic member 41.

The metal tube type embodiment of the invention, as shown in Fig. '1,offers the most practical structure where mechanical strength isdesired. The construction is similar to that used in metal vacuum tubes,the case 5I being welded to bottom steel disc 5a. Metal eyelet 58, isinserted into a hole punched in the disc 52, and welded into place toform a bottom header for the tube. The lead rod 59, together with asmall cylinder of glass 6I, is inserted in the eyelet. Metal exhausttubulation 62, is welded into place. Movable silver contact mounted onrod 55, which is welded to the thin top, 56, of metal tube 5I, iscontrolled by the movement of terminal rod 51, welded to the outside oftube 5I, directly opposite rod 55. Capsule I9, containing mercury isheated to the bursting point by short-circuiting of tungsten wire 29,connected to base 52 and shield 63. The circuit may be closed by movingrod 51 so as to cause contact 54 to move over against stationary contact53, mounted on terminal rod support 59. If magnetic operation of thecontact is desired, the actuating magnetic core can be mounted inside ofthe metal tube with the magnetic coil externallyv mounted.

While Fig. '1 is the only form of metal tube structure shown in thedrawing, the assemblies shown in Figs. 1-6 can also be used in metalhousings.

At the time the mercury is volatilized into the container, the contactbecomes coated with condensed mercury which arnalgamates with thecontact surface. Even though at normal room temperatures, the pressureof the mercury atmosphere in the bulb is only 0.0012 mm., there is acontinual migration of mercury to amalgamable metal parts, as can beobserved by the change in color of the copper heat absorbing pieces withtime. The initial condensation of the volatilized mercury on thecontacts reduces very materially the time that would otherwise berequired to completely amalgamate the contact surface sumciently to givethe surface tension and contact breaking effects of a mercury lm. Thegold plated contacts amalgamate the most rapidly, due to the high ainityof gold for mercury.

Having described my invention, what I claim as new and desire to secureby Letters Patent, is:

1. An electrical make and break device comprising an evacuated sealedchamber having therewithin a pair of solid cooperating contacts,

at least one of which is movable and at least one of which is formedfrom a metal amalgamable with mercury, a mercury atmosphere in saidchamber and a lm of mercury on at least one of said contacts.

2. An electrical make and break device comprising an evacuated sealedchamber having therewithin a pair of solid cooperating contacts. atleast one of which is movable and at least one of which has a workingface comprising an amalgam ot mercury, and a mercury atmosphere in saidchamber.

3. An electrical make and break device com- 'priaing an evacuated sealedchamber having .g therewithin a pair of solid cooperating contacts, atleast one of which is movable and at least one of whichhas a workingface comprising an amalgam ot mercury with one of the metals sold.silver. or copper, and a mercury atmosphere in 1. said chamber.

4. An electrical make and break device compriaing an evacuated sealedchamber having therewithin a pair ol solid cooperating contacts,

A at least one of which is movable and at least Iloneotwhichistormedfromamassoi'highheat condting metal having a workingface compriaing a mercury amalgam, and a mercury atmcsphere in saidchamber.

5. An electrical make and break device comlprising an evacuated sealedchamber having lthel'ewithin a pair of solid cooperating contacts, atleast one o! which is gravity controlled and at least one oi' which isformed from a metal amalgamable with mercury, a mercury atmosphere insaid chamber, and a illm of mercury on at least one ci said contacts.

8. An electrical make and break device comprlsing au evacuated sealedchamber having therewithin a pair of solid cooperating contacts, atleast one of which is thermostatically controlled. and at least one ofwhichis iormed from a metal amalgamabie with mercury, a mercuryatmosphere in said chamber, and a illm oi' mercury on at least one ofsaid contacts.

7. An electrical make and break device comprlsing an evacuated sealedchamber having thenewithin a pair oi solid cooperating contacts. atleast one of which is electro-magnetically controlled, and at least oneci' which is formed from a metal amalgamabie with mercury, a mercuryatmosphere in said chamber, and a nlm of mercury o at least one of saidcontacts.

8. An electrical make and break device comprising an evacuated sealedenvelope having therewithin a pair ot solid cooperating contacts. atleast one of which is movable and at least one oi' which is formed of ametal amalgamable with mercury, a mercury atmosphere in said chamber anda substantially immobile thin iilm of mercury on at least one of saidcontacts. terminals connected with said contacta extending from saidenvelope.

9. An electrical make and break device comprising an evacuated sealedmetal chamber having therewithin a pair of solid cooperating contacts.at least one o! which is movable and at least one of which is formedfrom a metal amalgamable with mercury. a mercury atmosphere in saidchamber, and a illm oi' mercury on at least one o! said contacts.

10. An electrical circuit Opening and closing device comprising a highlyevacuated sealed chamber containing a mercury vapor atmosphere. a pairof cooperating contacts therein, at least one o( which is movable, saidcontacts having working faces ot mercury amalgamated with a metal of thegold,l silver, copper mul. said contact faces being backed by relativelylarge heat dissipating of metal adapted to cool said contacts duringoperation so as to prevent complete volatilization of mercury therefrom.

1l. An electrical circuit opening and closing device comprising anevacuated air-tight chamber containing a mercury vapor atmosphere, apair oi solid hard cooperating contacts, at least one of which has aworking i'ace capable of tenaciously holding thereon a thin nim otmercury, a mass of high heat-conducting metal in direct intimate contactwith the circuit-breaking contact surfaces and having a heat capacityadequate to maintain the contact temperature below the point wherecomplete volatilixation ot the mercury would take place, and capable ofabsorbing and dissipating energy losses arising during operation of thedevice.

SAMUEL RUBEN.

